nope...

The server maintains a count of the number of items (messages+contacts+documents+etc...) in each folder, but I don't believe this count is surfaced in the web UI at present. If you'd really like to see this, please file a request in bugzilla!

I noticed in the webclient, int he upper right hand corner, you see a number (like 1-24) which just tells you which group of 25 messages you are viewing, but doesn't mention how any total messages there are. I'd like to see something like it saying "1-24 of 156"